Automatic sterilizing autoclave

ABSTRACT

AN AUTOCLAVE FOR STERILIZING ARTICLES BY STEAM UNDER PRESSURE WITH FULLY AUTOMATIC OPERATION THROUGHOUT A STERILIZING CYCLE. AN AUTOMATICALLY CONTROLLED VALVE IN THE AIR-STREAM EXHAUST PASSAGEWAY FROM THE AUTOCLAVE PRESSURE CHAMBER CLOSES THE EXHAUST PASSAGEWAY ONLY AT A PRESELECTED TEMPERATURE IN ORDER TO FIRST EXHAUST AIR FROM THE PRESSURE CHAMBER AT THE BEGINNING OF THE STERILIZING CYCLE, AND OPENS THE EXHAUST PASSAGEWAY AFTER A PREDETERMINED PERIOD AT THE END OF THE STERILIZING CYCLE, AT WHICH TIME THE HEATING ELEMENT IS ALSO AUTOMATICALLY CUT OFF. DURING THE STERILIZING CYCLE, NON-STERILE POCKETS OF AIR IN THE PRESSURE CHAMBER ARE AUTOMATICALLY PURGED THROUGH THE AIR-STREAM EXHAUST PASSAGEWAY BY THE AUTOMATIC CONTROL VALVE.

April 13, 1971 H. D. LARRO AUTOMATIC STERILI ZING AUTOCLAVE 4Sheets-Sheet 1 Filed Jan. 5. 1969 INVENTOR. HAROLD D. LARRO BY I FlG ..2

' ATTORNEYS April 1971 H. D. LARRO 3,574,529

' AUTOMATIC STERILIZING AuTocL vE' i Filed Jan. 5, 1969 4 Sheets- Sheet2 6 5 INVENTOR.

HAROLD o. LARRO BY FIG 4 7 ATTORNEYS April 13, 1971 H. D. LARRCYDJ3,574,529

AUTOMATIC S TERILIZ ING AUTOCL AVE med Jan. 3; 1969 ammwm a ll Q m In \mw I g H m 10\ 3 INVENTOR.

HAROLD D. LARRO v 7 f/hw ATTORNEYS April 13, 1971 H. D. LARRO AUTOMATIC.STERILIZING AU'IOCLAVE 4 Sheets-Sheet 4 INVENTOR. v HAROLD D. LARRQFiled Jan. 5.

ATTORNEYS United States Patent 3,574,529 AUTOMATIC STERILIZING AUTOCLAVEHarold D. Larro, 1865 SW. Fernwood Drive, Lake Oswego, Oreg. 97034 US.Cl. 21-94 12 Claims ABSTRACT UP THE DISCLOSURE An autoclave forsterilizing articles by steam under pressure with fully automaticoperation throughout a sterilizing cycle. An automatically controlledvalve in the air-steam exhaust passageway from the autoclave pressurechamber closes the exhaust passageway only at a preselected temperaturein order to first exhaust air from the pressure chamber at the beginningof the sterilizing cycle, and opens the exhaust passageway after apredetermined period at the end of the sterilizing cycle, at which timethe heating element is also automatically cut off. During thesterilizing cycle, non-sterile pockets of air in the pressure chamberare automatically purged through the air-steam exhaust passageway by theautomatic control valve.

This application is a continuation-in-part of United States patentapplication, Ser. No. 449,541, entitled sterilizing Autoclave, filed onApr. 20, 1965 and abandoned on Jan. 30, 1969.

This invention relates to a new and improved sterilizing autoclave forsterilizing by heat under pressure, medical, surgical and dentalinstruments and other articles and appliances.

It is an object of the present invention to provide. a new and improvedsterilizing autoclave which provides fully automatic operationthroughout a sterilizing cycle without attendance by an operator afterthe initial settings. A related object is to provide an autoclave withsafety features which permit such fully automatic operation.

A further object of the invention is to provide a fully automaticsterilizing autoclave which continuously purges pockets of non-sterileair within the pressure chamber during a sterilizing cycle in order tomaintain complete sterility throughout the autoclave pressure chamber.

In order to accomplish these results, the present invention contemplatesproviding an autoclave for sterilizing articles in which the air-steamexhaust passageway communicating with the autoclave sterilizing pressurechamber is controlled by an automatic valve for completely automaticoperation during a sterilizing cycle. To this end, the valve isoperatively coupled with a thermoswitch which operates the valve toclose the air-steam exhaust passageway at a preselected air-steamtemperature, so that as steam is produced at the beginning of thesterilizing cycle, residual air in the autoclave pressure chamber isexpelled through the air-steam exhaust passageway before it is closed bythe valve. The valve is also operatively coupled with a timer whichoperates the valve to open the air steam exhaust passageway after apredetermined period of sterilization at substantially constanttemperature and pressure to vent steam in the pressure chamber into acondensing tank. At the same time the timer switch also shuts oil theheating element which produces steam from water placed in the pressurechamber. In a preferred embodiment of the invention, the valve is astainless steel solenoid valve. A feature and advantage of the presentinvention resides in a design 3,574,529 Patented Apr. 13, 1971permitting reduced number of parts which may be formed of non-corrosivematerial to minimize maintenance and permit the use of tap water withoutdeterioration.

According to another aspect of the invention, the automaticallycontrolled valve in the air-steam exhaust passageway is operated duringthe sterilizing cycle to continuously purge pockets of non-sterile airor gas released from articles placed in the pressure chamber. To thisend, the heat sensor for the thermoswitch which controls the valve ispositioned coaxially within the air-steam exhaust passageway between theautoclave pressure chamber and valve. When a pocket of cool ornon-sterile air or gas enters the exhaust passageway after the valve hasclosed the passageway at the beginning of a sterilizing cycle, the heatsensor detects the drop in temperature, and activates the thermoswitchto operate the solenoid valve and open the air-steam exhaust passagewayuntil the pocket of cooler air has been released. As sterile steam againenters the exhaust passageway, the heat sensor of the thermoswitchdetects the rise in temperature and activates the thermoswitch tooperate the valve and close the air-steam exhaust passageway to therebypreserve the substantially constant temperature and pressure within theautoclave sterilizing chamber.

Other objects, features and advantages of the present invention willbecome apparent in the following specification and accompanyingdrawings.

In the drawings:

FIG. 1 is a fragmentary side view partially cut away of a sterilizingautoclave embodying the present invention.

FIG. 2 is a fragmentary side view partially cut away of the oppositeside of the autoclave shown in FIG. 1.

FIG. 3 is a front view of the autoclave showing the indicator andcontrol panel and door to the sterilizing chamber.

FIG. 4 is a schematic drawing of the electrical circuitry for thesterilizing autoclave.

FIG. 5 is a diagrammatic side view with the housing cut away of anothersterilizing autoclave according to the present invention.

FIG. 6 is an exploded view of the thermoswitch and sensor for theautoclave shown in FIG. 5.

FIG. 7 is a side view partially cut away of the thermoswitch.

In the sterilizing autoclave shown in FIG. 1 there is provided asterilizing pressure chamber 14 having an access door 12. Duringsterilizing operations, the access door 12 is tightened by means of adoor yoke 11 against a pressure sealing gasket 12a mounted on thechamber body 14. The door .12 and yoke 11 are designed to retain steamwithin the chamber at a pressure of at least 27 pounds, that required tosafely sterilize at normal altitudes. Leading from the bottom ofpressure chamber 14 is a single air-steam exhaust passageway 19 which iscoupled in series through a pressure release safety valve 18, solenoidvalve '6, and condensing coil 16. Distilled water condensed from steamin the pressure chamber collects in condenser tank 15 from which it maybe removed through drain cock 13. A thermoswitch 5 whose heat sensingelement is positioned in the condensing tank 15 operates the solenoidvalve 6 at a preselected temperature of air-steam exhausted into thecondensing tank to close the air-steam exhaust passageway 19.

Water is placed manually into the autoclave sterilizing chamber 14through the access door 12 which is closed after the articles to besterilized have also been placed in the chamber. Heating element 7,positioned inside chamber 14- at the bottom, is energized as hereinafterdescribed to produce steam from water placed in the chamber. As steam isproduced, the cool air filling the chamber is expelled through exhaustpassageway 19 to the condensing tank 15. As the cooler air has beencompletely exhausted, steam then passes through the exhaust passageway19 to the condensing tank 15. This increase in temperature is sensed bythe heat sensor of thermoswitch Which operates the solenoid valve 6 toclose the air-steam exhaust passageway 19. Sterilization then takesplace for a period determined by a timer switch 3. When the preselectedsterilization period has elapsed, timer switch 3 operates the solenoidvalve 6 to open the airsteam exhaust passageway 19 and vent the steam inthe pressure chamber 14. At the same time, timer switch 3 de-energizesthe heating element 7. During the sterilizing cycle, the temperature inpressure chamber 14 is monitored by thermostat 4 through a tubecommunicating with air-steam exhaust passageway 19 between the solenoidvalve 6 and the pressure chamber. Thermostat 4 regulates heating element7 to maintain a constant preselected temperature in the range of, forexample, 250 to 270 degrees. The pilot light 9 is lit only duringperiods when heating element 7 is energized. The pilot light 8 remainslit when the timer switch 3 is closed during a sterilizing cycle.

An integrated electrical circuit is provided for electrical control ofsolenoid valve 6 by thermoswitch 5 and timer switch 3 and for electricalcontrol of the heating element 7 by thermostat 4 and timer switch 3 ashereinafter described. A boil-dry switch 2 is positioned at the bottomof pressure chamber 14 as a safety feature to cut out supply of power tothe electrical circuit in the event that the quantity of water in thesterilizing chamber is insufficient. An additional safety feature of theautoclave is the pressure release safety valve 18, a conventionalspring-loaded safety valve which releases steam to the side of theautoclave when pressure exceeds a predetermined safe value and whichreseals itself after safe pressure level is restored. Such conventionalsafety valves are described in US. Pat. No. 2,526,974 and US. Pat. No.2,548,691.

Controls for setting the timer switch 3 and thermostat 4, and pilotlight indicators 8 and 9 are mounted on a control panel 10 at the frontof the autoclave as shown in FIG. 3. A conventional pressure gauge 17 isalso mounted on the front of the access door 12. Drain cock 113 fordraining distilled water from condensing tank is provided at the bottomof the control panel.

A schematic diagram of the unitary electrical circuit for automaticallycontrolling operation of the autoclave elements during a sterilizingcycle is shown in FIG. 4. The electrical circuit includes athree-pronged A.C. plug 1 for access to, for example, a 110-115 voltA.C. 50-60 cycle power source. All current through the electricalcircuit passes through the conventional boil-dry switch 2 which is athermostat type switch. In the event that insufficient water is presentin the sterilizing chamber, overheating of heating element 7 operatesthe boil-dry switch to open the entire circuit and cut off power. Allcurrent through the circuit also passes through timer switch 3, which isset on the control panel to close the electrical circuit for apreselected period of time of, for example, zero to 60 minutes. Fromtimer switch 3, the circuit is connected to provide several currentloops. One current loop passes through the solenoid coil of stainlesssteel solenoid valve 6 and thermoswitch 5. Thus, the valve, by means ofa solenoid coil, is controlled by both the thermoswitch 5 and timerswitch 3. The solenoid valve is adjusted so that the seat of the valveis normally open thereby leaving the air-steam exhaust passageway 19open to the condenser tank I15 which communicates with the atmosphere.When both the timer switch 3 and thermoswitch 5 are closed, permittingcurrent to pass through the solenoid coil of the solenoid valve, thevalve is operated to close the seat of the valve and thereby close theair-steam exhaust passageay 19 permitting pressure to build up withinpressure chamber 14. At the end of a sterilizing cycle when timer switch3 opens the electrical 4 circuit, the solenoid valve returns to itsnormally open position, thereby venting steam from the pressure chamber14 through the air-steam exhaust passageway 19 to the atmosphere viacondenser tank 15.

A second current loop from timer 3 passes through the thermostat 4 andheating element 7 to permit control of the heating element 7 by thethermostat 4. Thus, When timer switch 3 closes the circuit initiating asterilizing cycle, the heat sensing element of thermostat 4 monitors thetemperature in the sterilizing chamber through a tube communicating withthe pressure chamber to open and close the circuit to the heating coilto thereby maintain a constant preselected temperature. The thermostat 4is adapted to maintain temperature regulation in the sterilizing chamberof within, for example, A of a degree. Heating element 7 can bepositioned inside the sterilizing pressure chamber 114 at the bottom.

A third current loop from timer .3 passes through the pilot light 8 andback to the terminal strip 1, the pilot light 8 thereby indicating whenthe complete electrical circuit is under operation, i.e., when timerswitch 3 is closed. A final current loop from timer 3 passes through thethermostat 4, a second pilot light 9 connected in parallel with theheating coil 7 and then back to the terminal strip 1. Pilot light 9thereby indicates when the heating element 7 is energized by thermostat4.

Another sterilizing autoclave embodying the present invention isillustrated in FIGS. 5 through 7. According to this embodiment, there isprovided within a housing a sterilizing pressure chamber 51 having anaccess door 52 and a control panel 53 similar to that illustrated inFIGS. 1 through 3. A single air-steam exhaust passageway 55 is connectedto the bottom of pressure chamber 51 and passes in series adjacent apressure release safety valve 56, and through solenoid valve 57 andcondensing coil 58, which terminates in condensing tank 60,communicating with the atmosphere through a hole 6 1 in the housing 50of the autoclave.

According to this form of the invention, however, the thermoswitch 65,which electrically controls solenoid 57 is positioned so that the heatsensor or sensing element 76 of the thermoswitch communicates with theair-steam exhaust passageway 55 intermediate the sterilizing chamber 51and solenoid valve 57. Thus, whereas in the embodiment of the presentinvention previously described the heat sensitive element ofthermoswitch 5 was positioned in the condensing tank 15, according tothe form illustrated in FIGS. 5 through 7 the heat sensing element 76monitors the temperature of air-steam in the pressure chamber 51 beforeit reaches solenoid valve 57.

As in the previous embodiment described in FIGS. 1 through 4, there isprovided an electrical timer switch, not shown, which also controls thesolenoid valve 57 and a heating element positioned at the bottom of thesterilizing chamber 51, not shown herein. A thermostat -62 regulatespower to the heating coil as heretofore described to maintain apreselected constant temperature. Pilot light 63 is lit when the heatingelement is energized. An additional pilot light, not shown, indicateswhen the timer switch is closed in the manner heretofore described.Thus, the electrical circuitry for automatically controlling thesolenoid valve 57 and heating element for the autoclave illustrated inFIGS. 5 through 7 is the same as that shown in FIG. 4 with thecorresponding elements substituted.

A feature and advantage of the form of the invention shown in FIGS. '5through 7 resides in a continuous purg ing of cooler non-sterile pocketsof air developing in the pressure chamber during the sterilizing cycle.This continuous purging is accomplished by solenoid valve 57 underelectrical control of the thermoswitch -65. Solenoid valve 57 isadjusted so that the valve seat is normally open permitting a continuouspassageway between the chamber 51 and the atmosphere through condensingtank 60. Water is placed in the pressure chamber along with articles tobe sterilized and access door 52 is sealed. The

timer switch is turned on and set for the predetermined sterilizationperiod, thereby energizing the heating coil to generate steam in thepressure chamber. Cool air in the pressure chamber is displaced andvented through the air-steam exhaust passageway 55 through solenoidvalve 57 until steam enters the passageway. The increase in temperatureis sensed by the sensor of thermoswitch 65, which closes the electricalcircuit to the solenoid coil of valve 57 operating the valve to closethe seat of the valve and thereby close the air-steam exhaust passageway'55, permitting steam pressure to build up within the chamber 51. Thesterilizing cycle thereafter continues with temperature controlmaintained by thermostat 62 heretofore described.

During the sterilizing cycle, however, pockets of nonsterile cooler airmay develop or emerge from articles in the chamber being sterilized. Ifsuch non-sterile pockets of air develop, being heavier they will movedownward into the air-steam exhaust passageway 55. The decrease intemperature is sensed by the heat sensing element '76 of thermoswitch 65which opens the electrical circuit to the solenoid coil of valve 57, sothat the valve returns to its normally open seat position therebyopening the air-steam exhaust passageway 55 to vent the non-sterile airinto condensing tank 60. When steam at the sterilizing temperature againreaches the heat sensitive element of thermoswitch 65, the solenoidvalve is operated to close the seat of the valve and once again closethe airsteam exhaust passageway. As non-sterile pockets of air developduring the sterilizing cycle, they are continuously purged in the mannerdescribed above.

A more detailed illustration of the configuration and placement ofthermoswitch 65 is illustrated in FIGS. 6 and 7. The thermoswitch 65consists of an electrical switch 70 actuated by a pushbutton 71 to openor close the electrical connections between terminals 72. The switch ispivotally mounted on a frame 73 on an axis 74 and is biased by a spring75 in the direction of a heat sensing element 76, also rigidly mountedto frame 73. The heat sensing element 76 consists of an elongate tubularhousing 77 filled with an expandable heat sensitive material such asparacyeme. The heat sensitive material expands with increasingtemperature and contracts with decreasing temperature to respectivelyextend and retract a small piston 78 mounted in juxtaposition to thepushbutton 71 which actuates electrical switch 70. By means of anadjustable screw 80 the thermoswitch can be calibrated so that piston 78depresses pushbutton 71 at a preselected temperature. Screw 80 adjuststhe distance between the pushbutton 71 and piston 78 and operatesagainst bias of spring 75. In order to maintain the air-steam mixturefrom chamber '51 in intimate contact with the elongate tube 77 filledwith a heat sensitive material, tube 77 is coaxially enclosed by acollar 81, which is maintained in the air-steam exhaust passageway 55.The tube 77 containing heat sensitive material is spaced coaxiallywithin collar 81 by means of a threaded portion 82, which engagesinternal threads at the end of collar 81. Steam from pressure chamber 51enters the air-steam exhaust passageway 55 which communicates with oneend of the collar 81. The air-steam mixture is distributed around thetubular container 77 and thereafter passes out the air exhaust steampassageway 55 from the other end of collar 81. Thermoswitch 65 therebymaintains sensitive control over solenoid valve 57 for release orpurging of pockets of non-sterile air developing during a sterilizingcycle and for closing the valve upon contact with steam of thepreselected sterilizing temperature.

What is claimed is:

1. An autoclave comprising:

a pressure chamber having an access door to receive articles forsterilization and contain steam under pressure;

electrical heating means for producing steam from water placed in thepressure chamber;

a single air-steam exhaust passageway communicating with the inside ofthe pressure chamber and leading to the outside of the chamber; solenoidvalve in the air-steam exhaust passageway adapted to open and close saidpassageway, said valve biased in a normally open position; thermoswitchelectrically coupled with the solenoid valve to operate said valve andclose the air-steam exhaust passageway only at and above 'a preselectedair-steam temperature whereby air in the pressure chamber is expelledthrough the air-steam exhaust passageway by steam produced in thepressure chamber before the passageway is closed; and a timer switchelectrically coupled with said solenoid valve to operate said valve toopen the air-steam exhaust passageway after a predetermined time, saidtimer switch also electrically connected to the heating means tosimultaneously shut off said heating means at said predetermined time.

An autoclave comprising: pressure chamber adapted to receive articlesfor sterilization and contain steam under pressure; electrical heatingmeans for producing steam from water placed in the pressure chamber;single air-steam exhaust passageway communicating with the inside of thepressure chamber and leading to the outside of the chamber; solenoidvalve in the air-steam exhaust passageway adapted to open and close saidpassageway, said valve biased in a normally open position; thermoswitchelectrically coupled with the solenoid valve to operate said valve andclose the air-steam exhaust passageway only at and above a preselectedair-steam temperature whereby air in the pressure chamber is expelledthrough the air-steam exhaust passageway by steam produced in thepressure chamber before the passageway is closed; timer switchelectrically coupled with said solenoid valve to operate said valve toopen the air-steam passageway after a predetermined time, said timerswitch also connected to the heating means to simultaneously shut offsaid heating means at said predetermined time;

a thermostat electrically coupled with the heating means to maintain asubstantially constant temperature in the pressure chamber during thesterilization period;

a boil-dry switch electrically coupled with the heating means to preventoperation of the heating means when insufiicient water is present in thepressure chamber;

and an electrical circuit controlling operation of said autoclave, saidtimer switch and boil-dry switch connected in said electrical circuit toopen and close said circuit, said thermostat and heating means connectedin series along a first parallel leg of the electrical circuit from thetimer switch and boil-dry switch, said solenoid valve and thermoswitchconnected in series along a second parallel leg from the timer switchand boil-dry switch.

3. An autoclave as set forth in claim 2 wherein there also provided;

a first pilot light connected along a third parallel leg of the electriccircuit from the timer switch and boildry switch to indicate when saidswitches are closed and when a sterilizing cycle is underway;

and a second pilot light, said second pilot light connected in parallelacross the heating means in said circuit whereby said second pilot lightindicates when the heating means is activated.

4. An autoclave comprising:

a pressure chamber having an access door to receive articles forsterilization and contain steam under pressure;

means for providing steam in the pressure chamber;

a single air-steam exhaust passageway communicating with the inside ofthe pressure chamber and leading to the outside of the chamber;

a valve in the air-steam exhaust passageway adapted to open and closesaid passageway, said valve biased in a normally open position;

a thermoswitch operatively coupled with the valve to operate said valveand close the air-steam exhaust passageway only at and above apreselected air-steam temperature whereby air in the pressure chamber isexpelled through the air-steam exhaust passageway by steam provided inthe pressure chamber before the passageway is closed, said thermoswitchactuated by a heat sensitive element positioned within the airsteamexhaust passageway between the pressure chamber and the valve wherebypockets of air cooler than said preselected temperature areautomatically purged from the pressure chamber through the airsteamexhaust passageway and valve during a sterilizing cycle;

and a timer switch operatively coupled with said valve to operate saidvalve to open the air-steam exhaust passageway after a sterilizing cycleof predetermined period, said timer switch also operatively coupled tothe steam providing means to simultaneously shut off said means aftersaid predetermined period.

5. An autoclave as set forth in claim 4 wherein said air-steam exhaustpassageway communicates with the pressure chamber through the bottom ofsaid pressure chamber.

6. An autoclave as set forth in claim 4 wherein the heat sensitiveelement of said thermoswitch is an elongate element mounted coaxiallywithin and spaced from the walls of said air-steam exhaust passagewaywhereby the air-steam flow in the passageway is distributed around theheat sensitive element.

7. An autoclave comprising:

a pressure chamber adapted to receive articles for sterilization andcontain steam under pressure; electrical heating means for producingsteam from water placed in the pressure chamber;

a single air-steam exhaust passageway communicating with the inside ofthe pressure chamber and leading to the outside of the chamber;

a solenoid valve in the air-steam exhaust passageway adapted to closesaid passageway, said valve biased in a normally open position;

a thermoswitch electrically coupled with the solenoid valve to operatesaid valve and close the air-steam exhaust passageway only at and abovea preselected air-steam temperature whereby air in the pressure chamberis expelled through the air-steam exhaust passageway by steam providedin the pressure chamber before the passageway i closed, saidthermoswitch actuated by a heat sensitive element positioned within theair-steam exhaust passageway between the pressure chamber and thesolenoid valve whereby pockets of air cooler than said preselectedtemperature are automatically purged from the pressure chamber throughthe air-steam exhaust passageway and solenoid valve during a sterilizingcycle;

a timer switch electrically coupled with said solenoid valve to operatesaid valve to open the air-steam exhaust passageway after a sterilizingcycle of predetermined period, said timer switch also electricallyconnected to the heating means to simultaneously shut off said heatingmeans at said predetermined period;

a thermostat electrically coupled with the heating means to maintain asubstantially constant temperature in the pressure chamber during thesterilization period;

a boil-dry switch electrically coupled with the heating means to preventoperation of the heating means when insuflicient water is present in thepressure chamber; and an electrical circuit controlling operation ofsaid autoclave, said timer switch and boildry switch connected in saidelectrical circuit to open and close said circuit, said thermostat andheating means connected in series along a first parallel leg of theelectrical circuit from the timer switch and boil-dry switch, saidsolenoid valve and thermoswitch connected in series along a secondparallel leg from the timer switch and boil-dry switch.

8. An autoclave as set forth in claim 7 wherein said air-steam exhaustpassageway communicates with the pressure chamber through the bottom ofsaid pressure chamber.

9. An autoclave as set forth in claim 7 wherein the heat sensitiveelement of said thermoswitch is an elongate element mounted coaxiallywithin and spaced from the walls of said air-steam exhaust passagewaywhereby the air-steam flow in the passageway is distributed around theheat sensitive element.

10. In an automatic autoclave of the type having a pressure chamber forreceiving articles for sterilization and containing steam underpressure, means for providing steam in the pressure chamber; a singleair-steam exhaust passageway communicating with the inside of thepressure chamber and leading to the outside of the chamber; a solenoidvalve in the air-steam exhaust passageway adapted to open and close saidpassageway; and a thermoswitch electrically coupled with said solenoidvalve to operate said valve and close the air-steam exhaust passagewayonly at and above a preselected air-steam temperature whereby air in thepressure chamber is expelled through the air-steam exhaust passageway bysteam provided in the pressure chamber before the passageway is closed,said thermoswitch actuated by a heat sensitive element positioned withinthe air-steam exhaust passageway between the pressure chamber and thesolenoid valve,

said valve biased in a normally open position whereby pockets of aircooler than said preselected temperature are automatically purged fromthe pressure chamber through the air-steam exhaust passageway and valveduring a sterilizing cycle.

11. An autoclave as set forth in claim 10 wherein said air-steam exhaustpassageway communicates with the pressure chamber through the bottom ofsaid pressure chamber.

12. An autoclave as set forth in claim 10 wherein the heat sensitiveelement of said thermoswitch is an elongate element mounted coaxiallywithin and spaced from the walls of said air-steam exhaust passagewaywhereby the air-steam flow in the passageway is distributed around theheat sensitive element.

References Cited UNITED STATES PATENTS MORRIS O. WOLK, Primary ExaminerB. S. RICHMAN, Assistant Examiner US. Cl. X.R.

